1. Field of the Invention
The present invention relates to a method of increasing hydrocarbon production from a subterranean formation having impaired permeability as the result of well drilling or prior stimulation treatments.
2. Description of the Prior Art
Various procedures have been developed and utilized heretofore to increase the flow of hydrocarbons from hydrocarbon-containing subterranean formations penetrated by well bores. For example, a commonly used production stimulation technique involves creating and extending fractures in the subterranean formation to provide flow channels therein through which hydrocarbons flow from the formation to the well bore. The fractures are created by introducing a fracturing fluid into the formation at a flow rate which exerts a sufficient pressure on the formation to create and extend fractures therein. Solid fracture proppant materials, such as sand, are commonly suspended in the fracturing fluid so that upon introducing the fracturing fluid into the formation and creating and extending fractures therein, the proppant material is carried into the fractures and deposited therein whereby the fractures are prevented from closing due to subterranean forces when the introduction of the fracturing fluid has ceased.
In such formation fracturing and other production stimulation procedures, at least a portion of the stimulation fluid or fracturing fluid will leak off into the formation and will reduce the relative permeability of the invaded region of the formation. After fluid injection has ceased, imbibition will begin to alter the fluid distribution within the formation, and when production begins, the fluid will move from the formation into the fracture. It is important to leave the formation after treatment with the maximum permeability or conductivity possible whereby hydrocarbons contained in the formation will flow to the well bore with the least possible restriction. However, substantially all stimulation fluids or fracturing fluids, no matter how carefully they are selected, will do some damage to the formation adjacent to the fracture. In order to achieve maximum conductivity of hydrocarbons from subterranean formations, whether or not such formations have been fractured or otherwise stimulated, it has heretofore been the practice to cause the formation surfaces to remain water wet after treatment. Such water wetting has been shown to provide an improved flow of hydrocarbons through flow channels and capillaries in the magnitude of about three times greater than when the formation surfaces are hydrocarbon wet.
The water wetting of solid surfaces in subterranean hydrocarbon-containing formations as well as the surfaces of solid proppant material deposited therein has heretofore been accomplished using surfactants in the stimulation fluids or fracturing fluids whereby a layer of water or water and surfactant is spread over the solid surfaces. Such layers of water or water and surfactant are extremely viscous near the interface of the layer and the solid surface, and while the layer provides a slippage or lubricating effect at the interface thereof with hydrocarbons which decreases the resistance to flow, the layer reduces the effective diameter of capillaries and flow channels. This reduction of effective diameter restricts fluid flow, and in very small capillaries or flow channels becomes highly significant.
If the formation relative permeability has been damaged by the invasion of the stimulation fluid or fracturing fluid into the formation and this damage results in an increase in the capillary pressure in the damaged region, the capillary pressure in the damaged region then acts as a pressure sink drawing additional water to the damaged region. Unless the pressure drawdown upon attempting production is large enough to overcome the increased capillary pressure, a complete blocking of the formation in the damaged region will occur. Even when the pressure drawdown is sufficient to overcome the capillary pressure, production can be reduced because of the decrease in the capillary radius of the flow channels caused by the layer of water coating the solid surfaces in the formation.